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  1. #11
    Worker 11811's Avatar
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    I think I understand what you're saying but the reason I thought of a common exhaust is because I was wondering whether an air extractor might cause a reverse draw down the flue and, therefore, a buildup of combustion products inside the room.

    This was (and often still is) a concern for cinema projection rooms. The draw from the carbon arc lamp or xenon lamp had to be exhausted out of the room. (Soot and cancer causing combustion products from carbon arcs, ozone from xenon lamps and just plain heat extraction to keep the lamphouse from melting down.) The problem is that, unless you have air inlets to balance the pressure, you can end up with a reverse draw situation where air comes IN through non-operational stacks or else you will have negative pressure in the room. I have seen projection booths where the balancing fans stopped working and you couldn't open the doors to the room without a fight!

    So, my thought was to have a common vent, up the flue, with enough inlet air to balance the pressure in the space to keep the exhaust gas from the heater from backing up into the room.

    What do you think?
    Randy S.

    In girum imus nocte et consumimur igni.

    -----

    http://www.flickr.com/photos/randystankey/

  2. #12
    AgX
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    A good point! I forgot about that.

    The best way to avoid that is to give a lab its own fresh-air intake at least of the size of the exhaust. However that could mean getting too cold air in. Aside of an airheater or heat-recuperator, the other way would be to get the "fresh" air in by many "leaks" from the rest of the house. Preheated so to say. But if this doesn't work correctly a drain on that heater system might be produced, and exhaust from that may come in.

  3. #13

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    Don't forget that the flames in heating units also emit light.

  4. #14
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    Thank you ALL!! Yes I will put a carbon alarm in the room! good idea. I just wanted to hear from people who may have had this issue. I was going to use two bathroom fans over my sink. Venting right outside to keep the fumes down.

    Tim

  5. #15

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    Panasonic brand bathroom fans cost more but they are whisper quiet. You might want to do that since you'll be working in that room for hours at a time.
    Develop, stop, fix.... wait.... where's my film?

  6. #16

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    Putting an exhaust fan in a furnace room with normal flues on the appliances is a really bad idea. Unless you have positive pressure make up air into that room, you could backdraft both flues with your fan. Now if you have high efficient furnace and hot water tank with outside air supplied for combustion, you would be ok.
    Bob

  7. #17
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    Quote Originally Posted by Bob-D659 View Post
    Putting an exhaust fan in a furnace room with normal flues on the appliances is a really bad idea. Unless you have positive pressure make up air into that room, you could backdraft both flues with your fan. Now if you have high efficient furnace and hot water tank with outside air supplied for combustion, you would be ok.
    Yes Both my furnace and water tank is high efficient and I found out last night that my furnace has a electric start! (stupid I know just never has a reason to know until now) so with that being said. Do you think a bathroom fan is going to be ok?

    Thanks

  8. #18
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    In order for you all to see what I am talking about I added a few photos from this weekends demo. I taped out the door in one photo as I will be entering the darkroom from my office. I also taped out the floor where the new wall will go. As you can see it is adding some extra space as the little room I opened up had white pain on the floor. The new wall will be my wet side and I was thinking of a L shaped counter to work to my sink. As you can see the water and furnace takes up a bit of room and I REALLY wish they were some where else. Oh well I will work around them!
    Thanks
    Tim

  9. #19

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    Your furnace is ok, but the hw tank is a normal convection flue, so you really should have positive pressure air into the room.
    Bob

  10. #20
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    Quote Originally Posted by Worker 11811 View Post
    Do you think that ventilation for the darkroom and for the water heater could go hand in hand?
    Depends on how old the furnace/boiler is.

    I don't know about the regulations in Canada and the US but here, a boiler will either be a balanced flue or a fan assisted flue. In both cases, the flue is two co-axial pipes. Fresh air is drawn in around the outside and hot flue gases escape via the inside pipe.

    The whole of the combustion area is sealed from the room so if the gas is burning incorrectly and putting out CO or CO2, it will all be vented and will not enter the room.

    Also, any combustable gases within the room will not come into contact with the burner so will not ignite.

    However, if you have an old burner/furnace then this might not be the case.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

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